Chromatic Variability: Tracing Time Lags from X-Ray to Optical in AGN Light Curves

Sayak Moulic, Ryan Ray, Ayush Banerjee, Yash Rajput, Priyangshu Sarkar

Abstract: Active Galactic Nuclei (AGNs), powered by accreting supermassive black holes, exhibit complex variability across the electromagnetic spectrum. This review integrates theoretical models with findings from time-domain surveys and GRMHD simulations to explore the physical mechanisms driving such variability. Special attention is given to the role of accretion disk instabilities thermal, viscous, and magnetorotational - as well as the influence of magnetic flux eruptions. The study evaluates how changing accretion states and magnetic activity shape observable light curves, particularly in changing-look AGNs. Open questions are outlined to guide future inquiry, to develop a unified model of AGN variability applicable across mass scales and emission regimes. We review current theoretical models alongside observational findings from time-domain surveys and high-resolution GRMHD simulations, focusing on how changing accretion states and magnetic flux eruptions contribute to variability patterns. We also investigate how MRI turbulence may account for the transition timescales in changing-look active galactic nuclei (AGNs). Finally, we outline key open questions and suggest future directions for bridging theory with observation, aiming to develop a more unified framework of AGN variability that applies across quasars and lower-mass active black holes.

Keywords: AGN variability, accretion disk instabilities, Eddington ratio, GRMHD simulations, magnetorotational instability

How to Cite?: Sayak Moulic, Ryan Ray, Ayush Banerjee, Yash Rajput, Priyangshu Sarkar, "Chromatic Variability: Tracing Time Lags from X-Ray to Optical in AGN Light Curves", Volume 14 Issue 8, August 2025, International Journal of Science and Research (IJSR), Pages: 994-1003, https://www.ijsr.net/getabstract.php?paperid=SR25819112832, DOI: https://dx.doi.org/10.21275/SR25819112832